1. Field of the Invention
The present invention relates to a fuel cell system, and more particularly, to a cell voltage measurer of a fuel cell stack and a fuel cell system using the same, in which a wiring line is protected and its structure is simplified.
2. Discussion of Related Art
A fuel cell is a power generation system that directly transforms chemical energy of fuel into electric energy by an electrochemical reaction. For example, a fuel cell can generate electric energy by using a reaction of hydrogen and oxygen to produce water. Representative examples of a fuel cell include phosphate fuel cells, molten carbonate fuel cells, solid oxide fuel cells, polymer electrolyte membrane fuel cells, and alkaline fuel cells, according to the kinds of electrolytes used.
A polymer electrolyte membrane fuel cell (PEMFC) has a relatively high output performance and a relatively quick start and response time. Also, the PEMFC can operate at a relatively low temperature. As such, the PEMFC can be used as a transportable power source for a portable electronic apparatus or a vehicle, as well as a distributed power source such as a stationary power plant for a house or a public structure.
Further, a direct methanol fuel cell (DMFC) is similar to the PEMFC because it uses a solid polymer as an electrolyte. However, the DMFC differs from the PEMFC in that its stack can be directly supplied with a liquid fuel such as methanol (without a reformer therebetween). Since the DMFC does not need to use a reformer, it can be smaller in size than the PEMFC.
Generally, a fuel cell (e.g., a PEMFC or a DMFC) includes a stack. Here, the stack includes a membrane electrode assembly (MEA), and a separator or a bipolar plate to supply fuel and an oxidant to an anode electrode and a cathode electrode of the MEA, respectively. The MEA and the separator (or the bipolar plate) form a cell unit (or unit cell) and are alternately stacked to form the stack.
A fuel cell stack including a plurality of stacked cell units (or unit cells) can be deteriorated after a long usage time. However, the plurality of stacked cell units are not uniformly deteriorated due to differences in their structure or position. For example, the pressure of the fuel supplied to the cell unit adjacent to an anode inlet is higher than that supplied to the cell unit adjacent to an anode outlet, so that the cell unit adjacent to the anode inlet is stressed and deteriorated more than the cell unit adjacent to the anode outlet. Thus, the lifespan of the conventional fuel cell stack is shortened due to the differences of the deteriorations of the cell units. Most of the conventional fuel cell stack is continuously used as long as the stack outputs a voltage higher than a referenced (or predetermined) level even though a certain cell unit is more deteriorated than other cell units. However, the fuel cell stack may suddenly stop operating when the certain cell unit stop to operate due to the deterioration.